1. Field of the Invention
This invention relates to a novel class of polymeric stabilizers based on the reaction product of an unsaturated olefin polymer and a substituted aromatic or phenolic compound, and the use of these reaction products as stabilizers for olefin polymers.
2. Description of Related Art
Certain phenolic compounds and derivatives thereof have been used to stabilize olefin polymers against polymer breakdown caused by processing these polymers at high temperatures. Examples of such materials would include alkylated monophenols, alkylated hydroquinones, alkyl substituted bis phenols and hindered phenolic benzyl compounds.
Several problems are associated with the use of these materials. They are generally not very compatible with olefin polymers due to their aromatic structure and also due to the presence of one or more polar (hydroxy) substituents in the aromatic nucleus. Thus it may be difficult to uniformly disperse the phenolic stabilizer within the polymer matrix or prevent it from migrating out of the polymer. Secondly, these materials are quite volatile at temperatures at which the matrix polymer is processed and/or extruded, and consequently a significant loss of stabilizer may be realized during the polymer processing due to evaporation.
It has been proposed in the prior art that the problem of volatility and, to some degree, compatibility can be minimized by providing phenolic-based stabilizers which are themselves polymeric. For example, British patent specification 1483067 discloses polymeric stabilizers prepared by reacting a phenolic compound with a liquid polymeric material such as polypropylene or polybutene in the presence of a Friedel-Crafts type catalyst to provide a phenol compound alkylated with the polymer reactant. These polymer reaction products are said to have little volatility at temperatures employed in polymer processing (200.degree.-280.degree. C.) and to be more compatible with a polymer matrix because of suitable matching of the polymer chain joined to the molecule of the phenol and the matrix polymer.
Alkylated phenols similar to those described above are also disclosed in British Patent Specification 1159368 wherein the polymeric alkylating agent may also include low molecular weight liquid polypropylene as well as higher molecular weight polyolefins such as polybutene and butyl rubber.
The stabilizers referred to above suffer from the deficiency that they are either very low molecular weight amorphous materials (polymer Mn below about 500) or that the degree to which the phenolic compounds are alkylated is difficult to control. Also, in the case of British Specification 1,159,368, the positioning of the phenolic substituent groups along higher molecular weight polymer chains can not be readily tailored but is rather an arbitrary function of the reaction chemistry. These variables can effect the compatability of the polymeric stabilizers with the matrix olefin-based polymers to which they are added to impart stability, as well as the physical properties of the matrix polymers.